Injuries to the human knee joint are regrettably all too frequent, usually resulting from participation in some form of athletics, although of course they can arise in other ways. A healthy knee joint operates to provide forward and backward hinging motion of the lower leg (tibia) relative to the upper leg or thigh (femur), and also provides a certain degree of relative sliding motion, and a certain degree of tilting motion.
The knee joint consists basically of a large rounded knuckle, at the lower end of the femur, with a rearwardly directed radiussed portion, which terminates in a rearwardly directed rounded extension. The underside of the knuckle has a relatively large radiussed surface facing downwardly whereas the rearwardly directed extension has a shorter radius. The tibia in the lower leg has an enlarged upwardly directed surface. When the knee is straightened the larger radiussed portion of the femur rests directly on this upper end of the tibia.
However when the knee is hinged, the movement of the knee joint results a hinging action of the knuckle surface relative to the tibia, followed by a physical displacement of the femur knuckle relative to the tibia. In fact, a sliding action takes place between the two every time the knee is bent and straightened.
All of these complex movements, in a healthy knee joint, are controlled by a variety of ligaments connected to the bones and to muscle groups. When an injury occurs, one or more of these ligaments becomes either broken or separated from either its attachment to the bone or its attachment of the muscle group. In these cases, the knee is then substantially weaker, and can dislocate.
The basic facts surrounding knee injuries and the problems they cause are well known to the medical profession. Numerous attempts have been made to provide some form of prosthesis or knee support which can be attached to the leg above and below the knee, and which is provided with hinged joints allowing the knee to operate, under certain restrictions, and providing some support against movements which will tend to dislocate the knee. Generally speaking, however, these supports have been of relatively crude design. They are all based on the principle of an upper cuff to be strapped around the thigh, and a lower cuff to be strapped around the leg, and a pair of joint links extending between the lower and the upper cuffs on either side of the knee. Usually, the design provides for two double pivot link joints, one on each side of the knee brace, pivoting along two parallel axes, in an effort to simulate the actual movement of the knee.
In practise, however, these devices do not provide the function desired. When the knee is more or less straight or only slightly bent, then the average existing knee support provides a reasonable degree of support. However, as the knee bends progressively further, there is a hinging displacement which takes place in the knee joint and causes relative movement between the upper and lower leg. When this occurs, the standard knee support is incapable of conforming to such displacement. Instead, what happens is that the upper leg applies substantial pressure to the upper cuff, causing the upper cuff to become separated from the upper leg. When this occurs, the degree of support provided is substantially reduced. A more detailed explanation of the knee movements causing these problems will be given below.
A further problem in the design of standard knee supports is simply that of discomfort. When the knee is bent for any significant length of time for example, when driving a car, the pressure of the upper cuff on the thigh causes reduced blood circulation to the lower leg, and it is common for long distance drivers and truck drivers wearing such knee supports to in fact find that their lower leg and ankle and foot are completely numb after a long drive, and the joints swell up.
Eventually, the swelling of the joints become permanent.
A further problem caused by these standard knee supports is damage to the skin, especially of the upper leg. As the knee flexes and straightens out, there is a degree of relative movement between the upper leg and the upper cuff, setting up a rubbing action. It is in fact common for wearers of knee supports to use special pads and liners which fit between the knee support and the skin of the thigh. However, these only provide partial solutions to the problem. Where there is such relative movement on a frequent and constant basis, the problem of rubbing friction damaging the skin will always be there.
Finally, the design of the standard knee support, when it is worn properly and fitted tightly, provides significant restrictions on the movement of the knee, so that the knee cannot perform certain natural movements. In particular, the knee joint can no longer provide a twisting action and can no longer provide a sideways tilting action. Thus for example, a simple movement such as crossing the legs, becomes impossible for a person wearing a standard knee support which is fitted properly. Alternatively, if the knee brace is not tightly fitted to the leg, the dislocation of the knee can occur. Participation in many forms of athletics becomes impossible. Even running or jogging becomes impossible for many people wearing a standard knee support. The mere action of running causes a natural forward and backward translation movement between the two components of the knee joint, as will be described in detail below, which occur naturally in a healthy knee. However, this forward and backward translation simply cannot take place in an injured knee supported by the standard knee support, without there being some relative movement between the thigh and the upper cuff. In practise, a person jogging wearing a knee support on an injured knee finds that the upper cuff slops to and fro, allowing an opening to develop around the upper edge of the cuff. The fact that an opening has developed around the upper edge of the cuff is due to excessive pressure that has been caused by the back of the thigh against the back of the cuff. In other words, the thigh is trying to force the cuff to move in a way which is impossible for the cuff due to its crude design. What happens in effect during jogging, is that the upper cuff imposes an additional strain on the injured knee joint causing an improper translation of the two halves of the joint, so that when the person strides forward and lands on the injured leg, with the knee bent in the normal jogging position, the knee is already improperly stressed due to the standard knee support. The two portions of the knee joint at that moment are in fact displaced relative to one another into an unnatural position, and when the foot lands on the ground, extreme pain can be experienced in the supported knee. This pain results from the unusual stresses placed on the supported knee by the support itself. These stresses, as explained above, displace the upper knee joint relative to the lower knee joint into an improper position so that when the supported leg becomes the load bearing leg, the load is not transferred correctly from the upper leg to the lower leg.
In addition to the foregoing problems, many relatively simple leg movements were unsupported by the standard type of knee support. These included various movements in which the knee joint is subjected to a slight sideways tilt. This may be a simple movement such as crossing the legs when sitting in a chair, or it may happen in simple exercise programs, and relatively unstressful games such as tennis. In any of these situations where the injured knee was subjected to a sideways tilting movement or a sideways stress, the standard form of support did not provide support which was adequate, and dislocations of the already damaged knee joint were common.
A careful anatomical study of the problem has been made, starting with an examination of the actual movement of a healthy knee joint.
As generally described above, when the leg is straight, the lower larger radiussed surface of the femur joint rests on the flattened surface of the upwardly facing tibia joint supported by the lateral meniscus, and protected by the knee cap. The radius of curvature of the femur knuckle varies progressively from front to rear. The greater radius is on the forward portion, and the radius reduces on the rearward portion, so that when hinged onto the rearward portion the femur lifts slightly upwardly from the tibia. Thus, as soon as the knee is bent, a levering moment is set up by the rearward end of the femur, causing the femur to be displaced upwardly away from the tibia. Further movement causes rotation of the rounded smaller radiussed portion on the rearwardly directed free end of the femur joint, and a forward sliding movement of the knuckle along the surface of the tibia and the meniscus occurs, causing forward linear displacement of the femur relative to the tibia.
If such a knee joint is damaged, and is supported by a standard knee support, having a standard biaxial connecting link on either side, the initial levering moment of the femur joint relative to the tibia will attempt to draw the upper cuff of the support down along the surface of the thigh. Further bending of the knee, which causes rotation of the femur knuckle and sliding forward displacement, sets up considerable stresses on the underside of the upper cuff, usually where the upper cuff is strapped underneath the thigh, causing excessive pressure on the undersurface of the thigh. This in turn, will tend to lever the upper cuff away from the thigh, thereby losing virtually all support. Various designs of upper cuff have been proposed in an attempt to deal with this. Ideally the upper cuff should be of a fairly substantial design and of reasonable length to grasp a substantial portion of the upper thigh. However, the longer the upper cuff is made, the greater the problem. This is because a levering moment is set up between the strap, passing under the thigh, and the lower edge of the cuff which digs into the upper surface of the thigh. The longer the upper cuff is extended, the greater becomes the moment of this levering action. This causes undesired forward displacement of the femur joint knuckle along the surface of the tibia joint.
Attempts to overcome this have generally been directed to simply shortening or reshaping the upper cuff so that its engagement of the upper surface of the thigh was reduced in length, usually simply by cutting away a portion of the upper cuff, so as to relieve the pressure on the upper part of the thigh.
However, this simply still further reduced the support and did nothing to solve the problem.
It has now been recognised that the problems created by the vertical displacement of the femur, during initial movement, followed by lateral sliding displacement of the femur knuckle in the later knee movement, are not capable of being supported by the standard knee support. The standard knee support with its somewhat unscientific double axis biaxial joint had no means for accommodating a vertical displacement followed by a lateral transition of the knee joint. The standard knee support can simply accommodate a hinging movement forwardly and backwardly and nothing else. Since in fact the natural movement of the knee joint does not perform a simple hinging movement forward and backwardly, but moves in a much more complex way, then it is apparent that the standard knee support cannot provide adequate support for an injured knee.
The present invention, therefore, is directed to providing a knee support in which the joint action between the lower and upper cuff of the support is capable of conforming more precisely to the natural movement of the knee, and thus providing support for the injured knee over a much greater range of movement, and throughout various different types of movement, thereby enabling the wearer to take part in various normal activities such as sitting down, crossing the legs, driving a car and the like without inconvenience, and in fact enabling the wearer to take part in a number of athletic sports such as jogging, tennis, and the like, while being afforded a very considerable degree of improved support for the knee in a variety of different positions.